Thank you to Scott Goldberg for presenting the case of a man with anemia, diarrhea, and significant weight loss who was ultimately found to have a colonic stricture and fistula unveiling the diagnosis of Crohn’s disease. The case brought up a lot of questions about some of the diagnostic test we send and how to use and interpret them.

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Top Pearls:

The American Gastroenterological Association suggests that chronic diarrhea should be defined as three or more loose or watery stools daily lasting for four or more weeks

A malabsorption diarrhea can occur when someone has not been eating for a prolonged amount of time. This “refeeding diarrhea” results from decreased villous to crypt ratio in the bowel wall and reduced ability to absorb nutrients.

Strictures in the colon impair that tissues ability to perform the task of fluid reabsorption and can result in watery diarrhea

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Fecal Calprotectin:

What is it?

Fecal calprotectin is a zinc and calcium binding protein derived from neutrophils and monocytes

Why use it?

It is a marker of neutrophil activity. Levels are increased in intestinal inflammation and can help distinguish inflammatory from non-inflammatory causes of chronic diarrhea.

For now, consider as an adjunctive test, not a final say in deciding diagnosis. In “low prevalence” settings (i.e. primary care office for abdominal pain, consider as data to help rule out IBD). In “high prevalence” settings (i.e. GI doctors’ office), may be data to help rule in and consider additional testing)

Fecal WBC/Leukocytes:

What is it?

A gram stain of a stool sample that looks for the presence of leukocytes in stool

Why use it?

Well, consider not using it. A meta-analysis suggests that it has a peak sensitivity of 70% and a specificity of 50% (although this study was performed in children).

How to use it?

Don’t use this in the hospital. If you think someone has infectious diarrhea, you should complete an infectious diarrhea work-up. Of note, it is not a test that should be sent for hospital-acquired diarrhea (the lab does not offer it at Moffitt if patient has been admitted >72 hours).

Fecal Fat (Quantitative):

What is it?

Fecal fat is fat in the stool. Health individuals typical excrete less than 6grams of fat even when fat consumption is increased to 100-125 g of fat/day. There can be increases in fat excretion when people take laxatives or are having a very large amount of stool (1000g/day). In order to be accurate, the patient must eat 60-100gms of fat for 3 days prior to collection and during the collection period. Stool is typically collected over 72 hours

Why use it?

To determine if the patient is having diarrhea due to malabsorption.

How to use it?

A quantitative fecal fat >6g/day is abnormal and >20g/day is consistent with steatorrhea. If you can keep track of the dietary intake of fat, you can also calculate a fractional fat absorption (fat intake – fat output / fat intake). A value of >94% is normal.